S3, E19: A couple weeks after the group is expelled from Greendale, Abed starts to go insane and is busted by the cops for going through the Dean's trash. He is recommended to go to therapy and the rest of the group joins him for support. Through a series of flashbacks the therapists diagnoses Abed and whole group as insane and drops the bomb that there was never a Greendale in the first place. They have all been locked up in a mental institution their entire time at Greendale. Jeff quickly realizes the therapist is a lying quack and forces him to reveal that he's been working for Chang to get the group of his scent of deposing the Dean. This activates the group to go back to Greendale to reclaim their enrollment at school.